An usual heating system, in which the reinforcing wire fabric in a buildings's concrete floor slab serves also as an electric heating element, has been installed as a test in a building subject to normal use and under everyday conditions, including North Dakota winters which sometimes produce minus 40 degree temperatures. The double use of welded wired fabric in the floor slab (as reinforcement, and as heating element) is expected to represent a saving over the cost of the more conventional systems of radiant heating, such as copper tubing for circulating hot water, or especially manufactured electric resistance cables. The elimination of furnace equipment likewise cuts costs. Balanced against this, however, is the cost of the necessary transformers. Another economy incorporated in this design is that the floor grid will be energized primarily at night to store heat in the floor and underlying area, thereby eliminating an increase in the daytime demand factor. Baseboard type resistance heating is provided to supplement the stored heat during late afternoon hours. However, if required, a thermostat will override the preset schedule to energize the floor grid during daytime hours.